frc::AprilTagFieldLayout Class Reference

Class for representing a layout of AprilTags on a field and reading them from a JSON format. More...

#include <frc/apriltag/AprilTagFieldLayout.h>

Public Types
enum class	OriginPosition { kBlueAllianceWallRightSide , kRedAllianceWallRightSide }

Public Member Functions
	AprilTagFieldLayout ()=default
	AprilTagFieldLayout (std::string_view path)
	Construct a new AprilTagFieldLayout with values imported from a JSON file. More...
	AprilTagFieldLayout (std::vector< AprilTag > apriltags, units::meter_t fieldLength, units::meter_t fieldWidth)
	Construct a new AprilTagFieldLayout from a vector of AprilTag objects. More...
units::meter_t	GetFieldLength () const
	Returns the length of the field the layout is representing. More...
units::meter_t	GetFieldWidth () const
	Returns the length of the field the layout is representing. More...
std::vector< AprilTag >	GetTags () const
	Returns a vector of all the april tags used in this layout. More...
void	SetOrigin (OriginPosition origin)
	Sets the origin based on a predefined enumeration of coordinate frame origins. More...
void	SetOrigin (const Pose3d &origin)
	Sets the origin for tag pose transformation. More...
Pose3d	GetOrigin () const
	Returns the origin used for tag pose transformation. More...
std::optional< Pose3d >	GetTagPose (int ID) const
	Gets an AprilTag pose by its ID. More...
void	Serialize (std::string_view path)
	Serializes an AprilTagFieldLayout to a JSON file. More...
bool	operator== (const AprilTagFieldLayout &) const =default

Friends
WPILIB_DLLEXPORT void	to_json (wpi::json &json, const AprilTagFieldLayout &layout)
WPILIB_DLLEXPORT void	from_json (const wpi::json &json, AprilTagFieldLayout &layout)

Detailed Description

Class for representing a layout of AprilTags on a field and reading them from a JSON format.

The JSON format contains two top-level objects, "tags" and "field". The "tags" object is a list of all AprilTags contained within a layout. Each AprilTag serializes to a JSON object containing an ID and a Pose3d. The "field" object is a descriptor of the size of the field in meters with "width" and "length" values. This is to account for arbitrary field sizes when transforming the poses.

Pose3ds in the JSON are measured using the normal FRC coordinate system, NWU with the origin at the bottom-right corner of the blue alliance wall. SetOrigin(OriginPosition) can be used to change the poses returned from GetTagPose(int) to be from the perspective of a specific alliance.

Tag poses represent the center of the tag, with a zero rotation representing a tag that is upright and facing away from the (blue) alliance wall (that is, towards the opposing alliance).

Member Enumeration Documentation

OriginPosition

enum class frc::AprilTagFieldLayout::OriginPosition

strong

Enumerator
kBlueAllianceWallRightSide
kRedAllianceWallRightSide

Constructor & Destructor Documentation

AprilTagFieldLayout() [1/3]

frc::AprilTagFieldLayout::AprilTagFieldLayout ( )

default

AprilTagFieldLayout() [2/3]

frc::AprilTagFieldLayout::AprilTagFieldLayout ( std::string_view  path )

explicit

Construct a new AprilTagFieldLayout with values imported from a JSON file.

Parameters

path	Path of the JSON file to import from.

AprilTagFieldLayout() [3/3]

frc::AprilTagFieldLayout::AprilTagFieldLayout	(	std::vector< AprilTag >	apriltags,
		units::meter_t	fieldLength,
		units::meter_t	fieldWidth
	)

Construct a new AprilTagFieldLayout from a vector of AprilTag objects.

Parameters

apriltags	Vector of AprilTags.
fieldLength	Length of field the layout is representing.
fieldWidth	Width of field the layout is representing.

Member Function Documentation

GetFieldLength()

units::meter_t frc::AprilTagFieldLayout::GetFieldLength

(

)

const

Returns the length of the field the layout is representing.

Returns

length

GetFieldWidth()

units::meter_t frc::AprilTagFieldLayout::GetFieldWidth

(

)

const

Returns the length of the field the layout is representing.

Returns

width

GetOrigin()

Pose3d frc::AprilTagFieldLayout::GetOrigin

(

)

const

Returns the origin used for tag pose transformation.

Returns

the origin

GetTagPose()

std::optional< Pose3d > frc::AprilTagFieldLayout::GetTagPose

(

int

ID

)

const

Gets an AprilTag pose by its ID.

Parameters

ID	The ID of the tag.

Returns

The pose corresponding to the ID that was passed in or an empty optional if a tag with that ID is not found.

GetTags()

std::vector< AprilTag > frc::AprilTagFieldLayout::GetTags

(

)

const

Returns a vector of all the april tags used in this layout.

Returns

list of tags

operator==()

bool frc::AprilTagFieldLayout::operator== ( const AprilTagFieldLayout &  ) const

default

Serialize()

void frc::AprilTagFieldLayout::Serialize

(

std::string_view

path

)

Serializes an AprilTagFieldLayout to a JSON file.

Parameters

path	The path to write the JSON file to.

SetOrigin() [1/2]

void frc::AprilTagFieldLayout::SetOrigin

(

const Pose3d &

origin

)

Sets the origin for tag pose transformation.

This transforms the Pose3ds returned by GetTagPose(int) to return the correct pose relative to the provided origin.

Parameters

origin

The new origin for tag transformations

SetOrigin() [2/2]

void frc::AprilTagFieldLayout::SetOrigin

(

OriginPosition

origin

)

Sets the origin based on a predefined enumeration of coordinate frame origins.

The origins are calculated from the field dimensions.

This transforms the Pose3ds returned by GetTagPose(int) to return the correct pose relative to a predefined coordinate frame.

Parameters

origin

The predefined origin

Friends And Related Function Documentation

from_json

WPILIB_DLLEXPORT void from_json ( const wpi::json &  json, AprilTagFieldLayout &  layout  )

friend

to_json

WPILIB_DLLEXPORT void to_json ( wpi::json &  json, const AprilTagFieldLayout &  layout  )

friend

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The documentation for this class was generated from the following file:

• frc/apriltag/AprilTagFieldLayout.h